Optical amplifier evaluating method and optical amplifier evaluating apparatus

Abstract

In an optical amplifier evaluating system of this invention, a pulse method using optical modulators and a probe method are combined to obtain a gain G and noise figure NF of an optical fiber amplifier. A first optical modulator turns on and off signal light output from a first light source. An optical multiplexer multiplexes the optical signal turned on and off by the first optical modulator and probe light output from a second light source. This optical signal multiplexed by the optical multiplexer is selectively fed into an optical fiber amplifier. A controller properly switches optical path switches to allow an optical spectrum analyzer to measure (1) the light intensity of an input signal of the probe light to the optical fiber amplifier, (2) the light intensity in a region where signal light extracted from the output signal light from the optical fiber amplifier by a second optical modulator is in an OFF period and the probe light is output, and (3) the light intensity in a region where the signal light extracted by the second optical modulator is in the OFF period and no probe light is output. On the basis of measured light intensities (1), (2), and (3), the controller calculates the gain G and noise figure NF of the optical fiber amplifier. In this manner, the optical amplifier evaluating system of this invention can accurately obtain the gain G and noise figure NF of the optical fiber amplifier.

What is claimed is:  
     
       1. An optical amplifier evaluating apparatus comprising: 
       a first light source device for outputting rectangular signal light which is turned on and off at a predetermined period;  
       a second light source device for outputting probe light;  
       an optical multiplexer for multiplexing the probe light and the signal light output from said first light source device and outputting multiplexed light to an input terminal of an optical fiber amplifier as an object to be measured;  
       an optical modulator for extracting, from an output from an output terminal of said optical fiber amplifier, an output signal in an OFF period of the signal light;  
       a light intensity measuring device for measuring intensity of input light to an input terminal;  
       optical switching means for switching optical paths between said optical multiplexer, said optical fiber amplifier, said optical modulator, and the input terminal of said light intensity measuring device; and  
       a controller for switching said optical switching means such that said light intensity measuring device measures a light intensity (Pout) in a region where the output signal light from said optical fiber amplifier is in an OFF period and the probe light is output, a light intensity (Pase) in a region where the signal light is in the OFF period and the probe light is not output, and a light intensity (Pin) of an input signal of the probe light to said optical fiber amplifier, and for obtaining a gain of said optical fiber amplifier from values of the measured light intensities.  
     
     
       2. An optical amplifier evaluating apparatus according to claim  1 , wherein said second light source device comprises ON-OFF means for turning on and off the probe light, and said ON-OFF means inputs ON-OFF light to said optical multiplexer. 
     
     
       3. An optical amplifier evaluating apparatus according to claim  1 , wherein said controller obtains a noise figure from the values of the light intensities. 
     
     
       4. An optical amplifier evaluating apparatus according to claim  1 , wherein said second light source device comprises an optical attenuator, and an output from said optical attenuator i s input to said optical multiplexer. 
     
     
       5. An optical amplifier evaluating apparatus according to claim  2 , wherein said second light source device comprises an optical attenuator, and an output from said attenuator is input to said ON-OFF means. 
     
     
       6. An optical amplifier evaluating apparatus according to claim  1 , wherein said controller changes a frequency of the probe light from said second light source device. 
     
     
       7. An optical amplifier evaluating apparatus according to claim  1 , wherein said light intensity measuring device is a spectrum analyzer, and the probe light from said second light source device is composed of light having a plurality of frequencies. 
     
     
       8. An optical amplifier evaluating method comprising 
       multiplexing output rectangular signal light from a first light source with probe light from a second light source by an optical multiplexer and applying multiplexed light to an optical fiber amplifier as an object to be measured, and  
       extracting the signal light output from said optical fiber amplifier by an optical modulator and obtaining a gain and noise figure as wavelength characteristics of said optical fiber amplifier from a light intensity in a region where the signal light is in an OFF period and the probe light is output, a light intensity in a region where the signal light is in the OFF period and the probe light is not output, and a light intensity of an input signal of the probe light to said optical fiber amplifier.  
     
     
       9. An optical amplifier evaluating method comprising 
       multiplexing output rectangular signal light from a first light source with light, obtained after output probe light from a second light source is modulated by an optical modulator into a rectangular optical signal which is turned on and off at a predetermined period, by an optical multiplexer and applying multiplexed light to an optical fiber amplifier ( 5 ) as an object to be measured, and  
       extracting the signal light output from said optical fiber amplifier by another optical modulator and obtaining a gain and noise figure as wavelength characteristics of said optical fiber amplifier from a light intensity in a region where the signal light is in an OFF period and the probe light is output in an ON period, a light intensity in a region where the signal light is in the OFF period and the probe light is in the OFF period, and a light intensity of an input signal of the probe light to said optical fiber amplifier.  
     
     
       10. An optical amplifier evaluating apparatus comprising: 
       a first light source for outputting signal light;  
       a first optical modulator for modulating the signal light into a rectangular optical signal which is turned on and off at a predetermined period;  
       a second light source for outputting probe light, and an optical multiplexer for multiplexing the probe light and optical signal output from said modulator and selectively outputting multiplexed light to an input terminal of an optical fiber amplifier as an object to be measured;  
       optical path switching means for switching connection states of the input terminal and an output terminal of said optical fiber amplifier;  
       a second optical modulator for extracting the signal light switched by said optical path switching means and output from the output terminal of said optical fiber amplifier; and  
       a controller for controlling said first optical modulator, said second optical modulator, and said optical path switching means, and analyzing means for obtaining a light intensity in a region where the signal light is in an OFF period and the probe light is output, a light intensity in a region where the signal light is in the OFF period and the probe light is not output, and a light intensity of an input signal of the probe light to said optical fiber amplifier, thereby obtaining a gain and noise figure as wavelength characteristics of said optical fiber amplifier.  
     
     
       11. An optical amplifier evaluating apparatus according to claim  10 , further comprising a third optical modulator arranged between said second light source and said optical multiplexer to modulate the probe light output from said second light source into a rectangular optical signal which is turned on and off at a predetermined period. 
     
     
       12. An optical amplifier evaluating method comprising the steps of: 
       outputting rectangular signal light which is turned on and off at a predetermined period from a first light source device;  
       outputting probe light from a second light source device;  
       multiplexing the probe light and the signal light output from said first light source device by an optical multiplexer and outputting multiplexed light to an optical fiber amplifier as an object to be measured;  
       extracting, by an optical modulator, an output signal in an OFF period of the signal light from an output from an output terminal of said optical fiber amplifier;  
       measuring an intensity of input light to an input terminal by a light intensity measuring device;  
       switching optical paths between said optical multiplexer, said optical fiber amplifier, said optical modulator, and the input terminal of said light intensity measuring device by optical switching means; and  
       switching said optical switching means by a controller such that said light intensity measuring device measures a light intensity (Pout) in a region where the output signal light from said optical fiber amplifier is in an OFF period and the probe light is output, a light intensity (Pase) in a region where the signal light is in the OFF period and the probe light is not output, and a light intensity (Pin) of an input signal of the probe light to said optical fiber amplifier, thereby obtaining a gain of said optical fiber amplifier from values of the measured light intensities.